54 BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE, 



its density progressively decreases. From the facts ■whicli Mr. ISTasmytli brought 

 forward, it appears that water is not a special and singular exception in this 

 respect, but that, on the contrary, the phenomena in relation to change of density 

 (when near the point of solidification^ is shared with every substance with "which 

 we are at all familiar in a molten state, so entirely so, that Mr. Nasmyth felt him- 

 self warranted in propounding, as a general law, the one before stated, — namely, 

 that in every instance in which he has tested its eidstenee, he finds that a molten 

 substance is more dense, or specifically heavier, than the same substance in its un- 

 molten state. It is on account of this if we throw a piece of solid lead into a pot 

 of melted lead, the solid, or unmolten metal, will fioat in the fluid, or molten metal. 

 Mr. Nasmyth stated, that he found that this fact of the floating of the unmolten 

 substance in the molten holds true with every substance on which he has tested 

 the existence of the phenomenon in question. As, for instance, in the case of lead, 

 silver, copper, iron, zinc, tin, antimony, bismuth, glass, pitch, rosin, wax, tallow, 

 <&c. ; and that the same is the case with respect to alloys of metals and mixtures 

 of any of the above-named substances. Also, that the normal condition as to 

 density is resumed in most substances a little on the molten side of solidification, 

 and in a few cases the resumption of the normal condition occurs during the act of 

 solidification. He also stated that, from experiments which he had made, he had 

 reason to believe that by heating molten metals up to a temperature far beyond 

 their melting point, the point of maximum density was, as in the case of water, 

 at 40° about to be passed ; and that at such very elevated temperatures the nor- 

 mal state, as regards reduction of density by increase of temperature, was also 

 resumed, but that as yet he has not been able to test this point with such certainty 

 as to warrant his alluding further to its existence. 



A MATHEMATICAL INVESTIGATION OF THE rEOPORTION BETWEEN THE LENGTH RE- 

 QUIRED FOR AN ELECTRIC TELEGRAPH CABLE AND ITS SPECIFIC GRAVITY. — BY 

 CAPTAIN BLAKELY. 



The author showed, by the principles of the composition of motion, as a tele- 

 graph wire was payed out from a ship, the velocity which gravity would give it 

 would soon become uniform by the resistance of the water as its parts descended i 

 therefore, the descending part of the cable from the advancing ship to the part 

 of the cable which had reached and was supported upon the bottom, as he 

 showed, in very deep w^ater, say two miles or more, might stretch back six or more 

 miles from the ship. Now, unless a great strain was kept on the brake in the ship 

 where the cable was paying out, a strain which in the case of the Atlantic cable 

 had caused it to part, it was obvious from this demonstration that there must 

 always be what the sailor termed " slack " in the cable when it reached and lay on 

 the bottom, for the inclined length of the rope was always longer than the hori- 

 zontal length of the bottom on which it was intended to lie. The author then 

 proceeded to estimate, by mathematical formulaa, and numerically, the exact pro- 

 portion of these in several supposed depths of soundings, rapidity of paying out 

 and specific gravity of the cable, and came to the conclusion; that the only way of 

 lessening an evil, which must never be expected to be entirely got rid of, was by 

 increasing the speed of the vessel paying out the cable, and diminishing the spe- 

 cific gravity of the cable itself, so that it should sink gently to its final position. 



